An aircraft is generally equipped with air systems, in particular for cooling certain parts, comprising circuits which extend from at least one air inlet to at least one air outlet, passing through heat exchangers.
Technological progress means that cooling requirements are increasing. Thus, as engine temperatures rise, the amount of heat which must be removed follows an upward trend, leading to an increase in the flow rate of air used for cooling and/or in the temperature of the air discharged outside the aircraft.
Although specific grilles, such as those shown in the document FR-2,911,116, have been developed so as to limit the perturbations caused by these air systems, the increase in flow rate of air used for cooling has a generally negative influence on the aerodynamics of the aircraft. As a consequence, the increase in cooling requirements cannot be made up for simply by increasing the flow rate, such that the temperature of the discharged air stream tends to increase.
However, when this temperature exceeds a certain threshold, the problem arises that the exiting air stream comes into contact with certain portions of the outer surface of the aircraft, made of composite material.
So as to limit the temperature of the air stream in contact with the outer surface, a first solution consists in equipping the surface to be protected with devices which can be used to generate aerodynamic perturbations, as shown in the document FR-2,920,130, in order to mix the hot air of the stream with the surrounding cold air. Although this solution makes it possible to limit the risk of damage to the outer surface made of composite material, it affects the aerodynamics of the aeroplane.
A second solution consists in generating a film of cold air at the outer surface so as to insulate it from the hot air stream. In this case, the cold air is produced by a cold air source installed in the aircraft and discharged outside the aircraft via a cold air outlet which is close to the hot air outlet and offset with respect to the latter in the direction of the flow of air outside the aircraft. According to one embodiment, at the outer surface, a plate separates the hot air outlet from the cold air outlet.
This solution is not entirely satisfactory as it involves an additional energy requirement in order to produce the cold air and convey it towards the outlet. In addition, this solution is effective only over a restricted region to the rear of the hot air outlet. Finally, the plate used to separate the hot air and the cold air produces parasitic drag which affects the aerodynamics of the aircraft.